Rag stuffed in barrels of P-47's guns?

Hello. My mother recently found a photo of my late father, posing by the wing of what I believe is a P-47 "razorback", which the RAF designated a Thunderbolt Mk. I. He flew with 135 Sq. RAF during the first half of 1945, out of Jumchar and Akyab in Burma, at a time when they were using Thunderbolt I's.
What intrigues me is that there seems to be pieces of rag stuffed into the gun barrels behind his head. I'm aware that the RAF used doped tape (for flush mounted guns) or some sort of condom arrangement to keep foreign bodies out of the gun barrels, but this is a new one for me.
Can anyone explain what might have been going on?

If I've done this right, I've attached a small version of the whole picture, and a detail of the most visible gun barrel.

As it was in the Burma theatre, where everything was in short supply, I'd guess it was an easy, or convenient way, of sealing off the muzzles, using what is probably 'cotton waste', for lack of barrel caps. ('Cotton waste' was the general term used for the seemingly endless supply of wads of, literally, waste cotton threads and fibres, the 'swarf' from the mills, still abundant at the time. It was used as a general-purpose cleaning cloth, for hands, mopping-up oil/paint/fuel/grease spillages, polishing windscreens etc etc, and was a common sight not only in the Military, but also (in the UK at least) in every garage, service station, engineering shop etc, even up to the 1970's. It was normally multi-coloured, with red, blue,white and every other coloured threads, instantly recognisable to anyone of .. er.. a 'certain age').
The .50 cal Brownings on the P-47 were mounted in stainless steel blast tubes, of a slightly larger diameter than the 'standard' M2 perforated barrel jacket, with the actual barrel muzzle recessed within the tube and, not being a 'common' weapon in the RAF inventory, compared to the .303 Browning and 20mm Hispano, it's likely that the card or 'rubber' 'slip on' caps, or the alternative 'plugs' which fitted inside the barrel tubes, were not readily available.
I suspect that the caps used for the Spitfire's 20mm cannon muzzles would not be the required size, if in fact they were available, and taping-off the muzzles (again, if suitable tape was indeed available) would not be ideal, and would be time-consuming and wasteful, so, an easy and abundant alternative serves the same purpose.
As you probably know, the gun muzzles were 'sealed' for two reasons - to prevent the ingress of dust, debris or insects, whilst on the ground and during take-off, particularly important in the dusty conditions of the 'dry' season in this theatre, and also to prevent, or at least minimise, the effects of 'damp cold', where the drop in temperature at altitude, even despite gun heating (at the breech end of the weapon), could cause moisture to freeze in the barrels, invariably leading to a stoppage.
Obviously, a loose 'bung' of cotton waste, or even a purpose-designed muzzle cap, will not cause a back pressure (in the barrel) , and will literally be blown out when the first round passes down the barrel.
That said, it is, of course, entirely possible that the 'bungs' shown in the photo were just a temporary 'fix', until proper caps could be fitted !

Interesting pic. Perhaps flannelette to keep the barrels clean as tyrodtom suggests. I have seen pics of P47s with tape or discs in the blast tubes, so perhaps the photo shows either a shortage of tape, or that some flannelette was placed in the tubes first. On a very different scale, I used to place a small piece of oiled flannelette around my rifle muzzle before putting on a muzzle cap as the flannelette helped keep the muzzle cap secured.

Thanks for all the replies!
Re the shortages in Burma, that's certainly evident from the daily reports of the squadron (which I downloaded from the UK National Archive) - not only is there constant complaint about aircraft unserviceable for lack of spares, but they seemed to keep using the same typewriter ribbon until it was completely illegible ...

The photo is stamped on the back with words to the effect "Cleared for publication" (I don't have it in front of me at present, so can't be sure of the exact phrase). I've seen a number of posed looking photos from 135 Sq. from round about this time, although I think they've been from Chittagong. I wonder if there was an official photographer of some kind hanging around 135 Sq. in early 1945.
This led my mother to come up with a suggestion of her own. If my father had been selected to strike a heroic pose in front of an aircraft for some official publication, his friends might have stuffed the gun barrels out of pure mischief!